Time variability of sea surface parameters in the tropical Atlantic using satellite and in situ data

Abstract

The influence of the tropical Atlantic Ocean over the climate of Europe, Africa and America is well known today. However, several questions about high-frequency processes in this region remain open. This thesis addresses the characterisation of the diurnal and other short timescale variability of the meteo-ocean variables measured in the tropical Atlantic Ocean by the PIRATA array, as well as derived air-sea heat fluxes. By combining the complementarity and mitigating the disadvantages of using the high temporal resolution of in situ data in conjunction with the excellent spatial coverage of satellite based data, this work also aims to investigate the characteristics of the Tropical Instability Waves in the tropical Atlantic. The satellite data validation process used in this study assesses each of the buoys individually, to take into account possible regional biases.
A complete picture of the mean diurnal cycle and the seasonal variability of the diurnal signal is performed for the first time for the whole tropical Atlantic basin. The SST diurnal signal presents strong characteristics during the respective summer in both hemispheres. However, through the wavelet technique used in this analysis, a significant diurnal signal at the equator could be noticed during the second half of each year, indicating a possible modulation of the diurnal signal by processes with different timescales. It is suggested that Tropical Instability Waves could be one of these processes. The results presented here show that the TIW clearly vary their position and time of activity, depending on the degree of development of the equatorial cold tongue. The most active year analysed in this study was 2001, when the spectral characteristics could be observed as far north as 4oN. The imprints of the TIW are well marked in the wind fields, showing that clearly there are coupled mechanisms associated with the TIW. Moreover, this study confirms that a coupling mechanism suggested for the Pacific Ocean is also applicable to the tropical Atlantic basin. The measurements made by the TMI sensor, in conjunction with the Qscat wind data showed that the atmospheric fields are highly correlated with the SST fields at the timescale associated with the TIW.
The analysis of the cross-scale relationship suggests that the passage of instability waves might affect the diurnal amplitude of SST, skin-SST and latent heat flux. The mechanisms that interact on the eastern and western side of the equatorial Atlantic tend to be distinct, especially due to the local oceanographic and meteorological conditions, and due to the different level of TIW activity.

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